Tubing systems utilizing ferruled-type compression fittings are defined by maximum allowable working pressures for safe transport of media. These systems frequently handle dangerous gases and liquids that must be capable of withstanding ever-increasing pressures either from intentional system pressure requirements or from equipment failure, which may give rise to pressures unintended by the system designer. Allowable stresses for tubing systems are defined in Boiler & Pressure Vessel codes & Process Piping codes and defined by material and temperature. When provided with the tube outer diameter and wall thickness, the maximum allowable working pressure of a specific tube material at various temperatures can be calculated. Ferruled-type compression fittings suffer from a well-known problem relating to a maximum limit for tube wall thickness. Designs and geometries within the industry all maintain a limit to each size of ferruled-type compression fitting for a specified tubing diameter. For example, these limitations are typically defined in tubing data charts for each manufacturer of dual ferruled-type compression fittings. The performance for a particular fitting is defined by the relative size of the ferrules to the wall thickness of the tubing to be deformed. As the wall thickness of a particular size of tubing increases, physical limitations of the fitting are approached. That is, once a certain wall thickness of the tubing is exceeded, the fitting becomes incapable of maintaining a grip on the tubing, due to a lack of deformation of the tubing in contact with or adjacent to the rear ferrule nose. Many tubing systems utilizing ferruled-type compression fittings on the market have not changed designs in more than 40 years.
Moreover, the introduction of newer and stronger tube materials into such conventional ferruled-type compression fittings have resulted in inconsistent fitting performance and unforeseen failure modes, such as premature tube slippage or partial ferrule “bite” and even sheared threads in drive nuts.
What is needed are ferruled-type compression fittings that do not suffer from these drawbacks.